Earthicle and Its Discontents: A Historical Critical Review of Iron (Oxide) Particles Singly and Doubly Shelled with Silica and/or Carbon

Abstract

Earthicle was conceived as an astromimetic particle mimicking the stratified structure of Earth. Although earthicle can come in various compositional and structural forms, its seminal version consisted of a spherical nanoparticle with an iron core, a silica shell, and a carbon crust. This study provides a historical review of composite, core/shell particles composed of four different combinations of phases present in this original version of the earthicle, three of which are biphasic and one of which is triphasic: iron(oxide)/silica, iron(oxide)/carbon, silica/carbon, and iron(oxide)/silica/carbon. The connection of all four types of particles to materials of astrophysical origin found in interstellar and interplanetary space is discussed. The referred studies on the three biphasic compositions were selected on the basis of their conceptual and methodological innovativeness or originality in terms of the analytical data. In contrast, all studies that have reported so far on the synthesis, characterization, or application of the hybrid particles with the triphasic composition, along with a number of related studies, are reviewed. The chronological perspective adopted for both types of hybrid compositions, biphasic and triphasic, allowed for the deduction of past and present trends in the research of these composite systems but also for the extrapolation of probable future trends. For example, the interest in silica-coated iron (oxides) has been greater than that in other three core/shell systems, especially in biomedical studies, one reason being the difference in reactivity and in the favored oxidation state of the magnetic core under silica and under carbon. The early focus of research on silica-coated iron (oxides) was mostly on controlling the synthesis process, but as of the early 2000s the interest in controlling the properties and devising new applications for these systems became dominant among the scientific community. Carbon-coated silica particles have been the least studied and have had the least impact among the three biphasic combinations reviewed, especially in the biomedical field where their research has been virtually none. Revived briefly around 2010, the interest in them wound down soon thereafter in favor of more complex compositions. Still, the most complex hybrid composition reviewed here, comprising iron (oxide) particles shelled doubly, first with silica and then with carbon, was the least studied of all four multiphasic compositions elaborated here. However, unlike the ups and downs in the research on the biphasic compositions in the particulate form, the corresponding interest in these triphasic particles has been continually increasing, in spite of the comparatively low number of literature reports on them. This promising trend emerging from the literature search may go hand-in-hand with the ongoing global tendency to fabricate complex composite particle structures in search of novel properties arising from the sometimes theoretically predictable and sometimes serendipitous synergies be...

Predicting Destabilization in Salt-Containing Aqueous Reverse Micellar Colloidal Systems

“…A variety of important relationships intersecting natural phenomena and human engineered systems can be found within the field of colloid and emulsion science. For example, the flow of contaminants such as lead, mercury, and chromium in natural water sources occurs through colloidal transport processes. − Emulsions and microemulsions impact crude oil spills on natural water sources, − guiding engineers to develop methods to separate oil from water after these disasters occur. − New insights on the formation of particles, as disparate as atmospheric aerosols that begin as microlayer droplets at sea surface and mesoporous opal nanoparticles in shales from the Marcellus Formation, have been gained by making comparisons to microemulsion systems created in laboratories. , A critical intersection of natural phenomena and human engineering, reverse micellar water-in-oil (w/o) microemulsions, has been used in the creation of multilayered nanoparticles called earthicles, created specifically to mimic the structure and composition of the earth’s layers at a much smaller scale. − Thus, with colloidal chemistry reaching into so many aspects of earth and environmental science and engineering, continually deepening our understanding of the structure and stability of colloidal systems has an equally far-reaching impact on our ability to predict natural phenomena and chemical behaviors in complex environments.…”

Ag2CO3 containing magnetic nanocomposite as a powerful and recoverable catalyst for Knoevenagel condensation

“…Also due to poor chemical permeability, silica can prevent the destruction of MNPs in different chemical environments. Moreover, the abundant silanol groups on the silica surface provide suitable conditions for different types of modification 10 , 25 – 28 . Some of recently developed magnetic nanostructures with silica shells are Fe 3 O 4 @BOS@SB/In 29 , Fe 3 O 4 @SiO 2 @PMO 30 , Re–SiO 2 –Fe 3 O 4 31 , Mag@Ti-NOS 32 , Fe 3 O 4 @RF@void@PMO(IL)/Cu 33 , Fe 3 O 4 @SiO 2 @propyl‐ANDSA 34 and Fe 3 O 4 @Au@mSiO 2 -dsDNA/DOX 35 .…”